JPH10241148A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable small light transmittance, surface smoothing, high strength and high durability by forming non-magnetic particle powder of non-magnetic lower layer as a stylus type non-magnetic particle powder mainly composed of iron including Al of the particular amount into the particles and then forming magnetic particle powder of magnetic recording layer as the stylus type magnetic particle powder mainly composed of iron including Al of the particular amount. SOLUTION: A non-magnetic lower layer is formed on a non-magnetic carrier with non-magnetic particle powder and binder and a magnetic recording layer is then formed thereon with magnetic particle powder and binder. The non-magnetic particle powder includes, within particle, Al of 0.05 to 50wt.% in terms of Al. As the stylus type non- magnetic particle powder mainly composed of iron covering the particle surface with any one of the hydroxide or oxide of Al, Si, it improves durability of the medium itself and also improve dispersion property with good affinity with the binder. Moreover, the magnetic particle powder is formed as the stylus type metal magnetic particle powder mainly composed of iron allowing existence of Al of 0.05 to 10wt.% in terms of Al. In this case, Al is included uniformly up to the surface from the center to form the covering layer on the particle surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION An object of the present invention is to provide a magnetic recording medium having a small light transmittance, a smooth surface, a high strength, and excellent durability.

[0002]

2. Description of the Related Art In recent years, as long-term recording and miniaturization of video and audio magnetic recording / reproducing devices have progressed, the performance of magnetic recording media such as magnetic tapes and magnetic disks has been improved. There is an increasing demand for higher performance, higher output characteristics, especially improved frequency characteristics, and lower noise.

Various attempts have been made to improve these various properties of the magnetic recording medium, from both aspects of improving the performance of the magnetic particle powder and reducing the thickness of the magnetic recording layer.

[0004] First, the performance improvement of magnetic particle powder will be described.

[0005] The characteristics of the magnetic particle powder suitable for satisfying the above requirements for the magnetic recording medium are to have a high coercive force and a large saturation magnetization.

In recent years, needle-like metal magnetic particles containing iron as a main component obtained by heating and reducing needle-like goethite particles or needle-like hematite particles in a reducing gas as magnetic particle powder suitable for high-output and high-density recording. Powders are widely used.

Next, the thickness reduction of the magnetic recording layer will be described.

In recent years, the demand for higher image quality and higher image quality of video tapes has been increasing more and more, and the frequency of a carrier signal to be recorded is higher than that of conventional video tapes. That is, the wavelength shifts to the short wavelength region, and as a result, the magnetization depth from the surface of the magnetic tape becomes extremely shallow.

In order to improve the high output characteristics of a magnetic recording medium, especially the S / N ratio, for a short wavelength signal, it is strongly required to make the magnetic recording layer thinner. This fact is described in, for example, “‥ Development of Magnetic Materials and Technology for Highly Dispersing Magnetic Powder” published by Sogo Gijutsu Center (1982), p.
The condition for high-density recording in a coating type tape is to be able to maintain high output characteristics with low noise for a short wavelength signal. For this purpose, both the coercive force Hc and the residual magnetization Br are large. And the thickness of the coating film must be thinner. ‥‥ ”.

As the thickness of the magnetic recording layer has been reduced, several problems have arisen. First, there is a problem of smoothing and uneven thickness of the magnetic recording layer. As is well known, in order to make the magnetic recording layer smooth and free of thickness unevenness, the surface of the base film must also be smooth. . This fact can be found, for example, in “Implementation of Engineering Information Center,“ Magnetic Tape-Factor / Wear Occurrence Factors and Trouble Measures for Head Running System-Comprehensive Technical Data Collection (hereinafter referred to as “Comprehensive Technical Data Collection”) ”(Showa 62
Years) p. 180 and p. 181 "The surface roughness of the magnetic layer after hardening strongly depends on the surface roughness (back surface roughness) of the base, and both are almost proportional to each other. As the surface of the base is made smoother, a uniform and large head output is obtained and the S / N is improved.

Second, the thickness of the base film has also been reduced as in the case of the magnetic layer, and as a result, the strength of the base film has become a problem. This fact is described, for example, in the above-mentioned “Development of Magnetic Materials and Technology for Highly Dispersing Magnetic Particles” on page 77, “‥‥ High Density Recording is a major theme that has been imposed on current magnetic tapes. This is important in reducing the length of the tape to reduce the size of the cassette and for long-time recording, which requires reducing the thickness of the film base. The stiffness of the tape suddenly decreases as the thickness decreases, making it difficult for the recorder to run smoothly.
It is greatly desired to improve the stiffness in both width directions. ‥‥ ”.

By the way, at present, the determination of the end of a magnetic tape of a magnetic recording medium such as a video tape is performed by detecting a portion of the magnetic recording medium having a high light transmittance by a video deck. As the light transmittance of the entire magnetic recording layer increases as the thickness of the magnetic recording medium becomes thinner and the magnetic particles dispersed in the magnetic recording layer become ultrafine, the detection by the video deck becomes difficult. The light transmittance is reduced by adding carbon black or the like to the layer. Therefore, in current video tapes, the addition of carbon black or the like to the magnetic recording layer is indispensable.

However, adding a large amount of non-magnetic carbon black or the like not only hinders high-density recording, but also hinders thinning. In order to make the magnetization depth from the surface of the magnetic tape shallower and to further reduce the thickness of the magnetic tape, it is strongly required to reduce the amount of non-magnetic particles such as carbon black added to the magnetic recording layer as much as possible. I have.

Therefore, there is a strong demand for a magnetic recording medium having a small light transmittance even if the amount of carbon black added to the magnetic recording layer is reduced, and from this point, there is also a strong demand for improvement of the substrate.

Furthermore, there is no limit to the recent demand for higher performance of magnetic recording media, and with the aforementioned thinner magnetic recording layer and thinner non-magnetic support, the surface of magnetic recording layer and magnetic Since the durability of the recording medium itself decreases, there is a strong demand for improving the durability of the magnetic recording layer surface and the durability of the magnetic recording medium itself.

This fact is described in Japanese Unexamined Patent Publication No. Hei 5-298679, "‥‥ Recently, with the development of magnetic recording, the demand for high image quality and high sound quality has been increasing more and more.
In particular, the ferromagnetic powder has been reduced in particle size and density, and the noise has been reduced by smoothing the surface of the magnetic tape.
/ N is required to be increased. However, as the friction coefficient of the contact between the magnetic layer and the device system increases during the running of the magnetic tape, the magnetic layer of the magnetic recording medium is likely to be damaged or the magnetic layer to be peeled off in a short time use. is there. Particularly, in the case of a video tape, since the video head and the magnetic recording medium run while contacting each other at a high speed, the ferromagnetic powder tends to fall off the magnetic layer, which causes clogging of the magnetic head. Therefore, it is desired to improve the running durability of the magnetic layer of the magnetic recording medium. It is clear from the description “‥‥”.

With the thinning of the magnetic recording layer and the thinning of the non-magnetic support, various attempts have been made to improve the base for forming the magnetic recording layer, and a non-magnetic support such as a base film has been developed. At least one underlayer (hereinafter, referred to as a nonmagnetic underlayer) formed by dispersing iron-based nonmagnetic particles such as hematite particles and ferric hydroxide particles in a binder is provided on the body. This has been done and has already been put to practical use. (Japanese Patent Publication No. 6-93297, JP-A-62-1
59338, JP-A-63-187418,
JP-A-4-167225, JP-A-4-32591
5, JP-A-5-73882, JP-A-5-18
2177, JP-A-5-347017, JP-A-6-60362, etc.)

[0018]

As the thickness of the magnetic recording layer is reduced, as well as the thickness of the nonmagnetic support, the light transmittance is low, the surface is smooth, the strength is high, and the durability is low. An excellent magnetic recording medium is currently most demanded, but a magnetic recording medium that sufficiently satisfies such characteristics has not yet been obtained.

That is, a magnetic recording medium manufactured using a substrate having a non-magnetic underlayer formed by dispersing a non-magnetic powder in a binder resin on a non-magnetic support has a low light transmittance and a smooth surface. Thus, although the strength is high, there is a problem that the durability is poor.

This fact can be explained by the fact that in Japanese Patent Application Laid-Open No. 5-182177, "(1) If a thick non-magnetic undercoat layer is provided on the surface of the support and then the magnetic layer is provided as the upper layer, the surface roughness of the support is reduced. However, there is a problem that the wear and durability of the head are not improved because the thermosetting resin is used as the binder as the non-magnetic lower layer so that the lower layer is hardened. However, this is because friction between the magnetic layer and the head and contact with other members are performed in an unbuffered state, and the magnetic recording medium having such a lower layer is slightly less flexible. it is conceivable that.‥‥"
It is as described.

Therefore, an object of the present invention is to provide a magnetic recording medium having a small light transmittance, a smooth surface, a high strength, and excellent durability.

[0022]

The above technical object can be achieved by the present invention as described below.

That is, the present invention relates to a nonmagnetic underlayer containing a nonmagnetic support, a nonmagnetic particle powder formed on the nonmagnetic support and a binder resin, and a magnetic layer formed on the nonmagnetic underlayer. In a magnetic recording medium comprising a particle recording powder and a magnetic recording layer containing a binder resin, the non-magnetic particle powder is mainly composed of iron containing 0.05 to 50% by weight of aluminum in terms of Al inside the particle. Wherein the magnetic particle powder is a needle-shaped metal magnetic particle powder containing iron as a main component in which 0.05 to 10% by weight of aluminum is present in terms of Al. It is a magnetic recording medium characterized by the following.

The present invention also provides a non-magnetic underlayer containing a non-magnetic support, a non-magnetic particle powder formed on the non-magnetic support, and a binder resin; and a non-magnetic under layer formed on the non-magnetic under layer. In a magnetic recording medium comprising a particle recording powder and a magnetic recording layer containing a binder resin, the non-magnetic particle powder contains 0.05 to 50% by weight of aluminum in terms of Al inside the particle, and water of aluminum is used. Oxide, oxide of aluminum, acicular nonmagnetic particle powder containing iron as a main component, the particle surface of which is coated with at least one of hydroxide of silicon and oxide of silicon, wherein the magnetic particle powder Is Al
A magnetic recording medium characterized in that it is a needle-shaped metal magnetic particle powder containing iron as a main component in which 0.05 to 10% by weight of aluminum is present in conversion.

The configuration of the present invention will be described in more detail as follows.

First, the magnetic recording medium according to the present invention will be described.

As the non-magnetic particle powder containing iron as a main component in the present invention, hydrated ferric oxide particles such as acicular goethite (α-FeOOH) particles and acicular hematite particles can be used. And 0.05 to 50% by weight of aluminum in terms of Al is almost uniformly contained inside the particles.

The acicular goethite particles containing aluminum almost uniformly inside the particles are, as described later in detail, a ferrous salt and any one of alkali hydroxide, alkali carbonate and alkali hydroxide / alkali carbonate. When an oxygen-containing gas such as air is passed through a suspension containing an iron-containing precipitate such as iron hydroxide or iron carbonate obtained by the reaction using the gas to form needle-like goethite particles, oxygen such as air is used. It can be obtained by allowing an aluminum compound to exist before passing the contained gas.

The acicular goethite particles thus obtained are particles containing aluminum substantially uniformly from the center of the particles to the surface of the particles.

Hematite particles containing aluminum almost uniformly inside the particles can be obtained by heating and dehydrating the goethite particles containing aluminum almost uniformly inside the particles.

The heating and dehydrating temperature is about 250 to 800 ° C. In consideration of the degree of densification of the acicular hematite particles containing aluminum uniformly inside the obtained particles, the particles are heated and dehydrated at 550 to 800 ° C. The obtained high-density acicular hematite particles are more preferable.

In particular, in the case of heating and dehydrating at a high temperature of 550 ° C. or more, as is well known, prior to the heating and dehydration of the acicular goethite particles, the surface of the acicular goethite particles is coated with a sintering inhibitor in advance. Preferably.

Examples of the sintering inhibitor include phosphorus compounds such as sodium hexametaphosphate, polyphosphoric acid, and orthophosphoric acid which are commonly used, No. 3 water glass, silicon compounds such as sodium orthosilicate, sodium metasilicate and colloidal silica, and boric acid. Use of boron compounds such as aluminum acetate, aluminum sulfate, aluminum chloride, aluminum chloride, aluminum nitrate, etc., alkali aluminates such as sodium aluminate, alumina sol, aluminum compounds such as aluminum hydroxide, and titanium compounds such as titanyl sulfate can do.

The amount of the sintering inhibitor present on the surface of the acicular non-magnetic particles containing iron as a main component is 0.0 to the total weight of the particles.
It is about 5 to 10% by weight.

When the amount of aluminum contained in the particles is less than 0.05% by weight in terms of Al with respect to the acicular nonmagnetic particles containing iron as a main component, the obtained magnetic recording medium has sufficient durability. Does not have the property. When the content exceeds 50% by weight, the obtained magnetic recording medium has sufficient durability, but the effect is saturated, and there is no point in containing more than necessary. Considering the durability of the magnetic recording medium, the content is preferably 0.5 to 50% by weight. More preferably, the content is 1.0 to 50% by weight.

The needle-shaped non-magnetic particles containing iron as a main component in the present invention may be made of at least one of aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide, if necessary. May be coated. The needle-shaped nonmagnetic particles mainly composed of iron whose particle surface is coated with these surface coatings are well compatible with the binder resin when dispersed in a vehicle, and the desired dispersibility can be easily obtained. Easily.

The amount of the surface coating is based on the total weight of the particles in terms of Al in the case of aluminum hydroxide or aluminum oxide, and in terms of SiO _{2 in} the case of silicon hydroxide or silicon oxide. On the other hand, 0.01 to 50% by weight is preferable. When the amount is less than 0.01% by weight, the effect of improving the dispersibility by coating is difficult to be obtained, and when the amount exceeds 50% by weight, the effect of coating is saturated, so that there is no point in adding more than necessary. Considering the dispersibility and productivity in the vehicle,
0.05-20% by weight is more preferred.

In the coating treatment, an aluminum compound is added to an aqueous suspension obtained by dispersing a cake, slurry, or dry powder of acicular goethite particles or acicular hematite particles in an aqueous solution.
By adding the silicon compound or both compounds and mixing and stirring, or if necessary, by adjusting the pH value, on the particle surface of the acicular hematite particles, a hydroxide of aluminum, an oxide of aluminum, A silicon hydroxide and a silicon oxide may be applied, followed by filtration, washing with water, drying and pulverization. If necessary,
Degassing / consolidation processing may be performed.

As the aluminum compound in the coating treatment, the same aluminum compound as that described above can be used.

The addition amount of the aluminum compound is 0.01 to 50% by weight in terms of Al with respect to the acicular nonmagnetic particle powder. If the amount is less than 0.01% by weight, the dispersion in the vehicle is insufficient, and if it exceeds 50% by weight, the coating effect is saturated, and there is no point in adding more than necessary.

As the silicon compound in the coating treatment,
The same sintering inhibitor as described above can be used.

The addition amount of the silicon compound is 0.01 to 50% by weight in terms of SiO ₂ with respect to the acicular nonmagnetic particle powder. If the amount is less than 0.01% by weight, the dispersion in the vehicle is insufficient, and if it exceeds 50% by weight, the coating effect is saturated, and there is no point in adding more than necessary.

When the aluminum compound and the silicon compound are used in combination, A
It is preferable that the total amount of the amount in terms of 1 and the amount in terms of SiO ₂ is 0.01 to 50% by weight.

The acicular nonmagnetic particles containing iron as a main component according to the present invention have an axial ratio (average major axis diameter: average minor axis diameter;
Simply referred to as "axial ratio". ) Is at least 2: 1, preferably 3:
One or more particles are preferred. Considering the dispersibility in the vehicle, the upper limit is 20: 1 or less, preferably 1: 1.
Particles of 0: 1 or less are preferred. Here, the acicular particles are
Needle-shaped, as well as spindle-shaped, rice-granular, etc. are meant.

When the axial ratio is less than 2, it becomes difficult to obtain a desired coating film strength.

In the present invention, the average major axis diameter of the needle-shaped nonmagnetic particle powder containing iron as a main component is 0.3 μm or less. If the average major axis diameter exceeds 0.3 μm, the particle size is too large, which impairs the surface smoothness of the coating film. If the average major axis diameter of the acicular nonmagnetic particles containing iron as a main component is less than 0.005 μm, dispersion in the vehicle becomes difficult. Considering the dispersibility in the vehicle and the surface smoothness of the coating film, the thickness is preferably 0.02 to 0.2 μm.

The needle-shaped nonmagnetic particles containing iron as a main component in the present invention preferably have an average minor axis diameter of 0.0025 to 0.15 μm. If the thickness is less than 0.0025 μm, dispersion in a vehicle becomes difficult, which is not preferable. If the average minor axis diameter exceeds 0.15 μm, the particle size is too large, which impairs the surface smoothness of the coating film, which is not preferable. Considering the dispersibility in the vehicle and the surface smoothness of the coating film, the thickness is preferably 0.01 to 0.10 μm.

The acicular goethite particles as the acicular nonmagnetic particles containing iron as a main component in the present invention preferably have a BET specific surface area value of 50 m ² / g or more. 50m ²
If it is less than / g, the surface smoothness of the coating film is adversely affected. It is preferably at least 70 m ² / g, more preferably 80 m ² / g.
m ² / g or more, and its upper limit is 300 m ² / g. Considering the dispersibility in the vehicle, it is preferably at most 250 m ² / g, more preferably at most 200 m ² / g.

The acicular hematite particles as the acicular nonmagnetic particles containing iron as a main component in the present invention preferably have a BET specific surface area value of 35 m ² / g or more. 35m ²
If it is less than / g, the hematite particles are coarse or particles are sintered between the particles and between the particles, which adversely affects the surface smoothness of the coating film. Preferably 4
0 m ² / g or more, more preferably 45 m ² / g or more, and the upper limit is 300 m ² / g. Considering the dispersibility in the vehicle, it is preferably 100 m ² / g or less, more preferably 80 m ² / g or less.

The iron-based acicular non-magnetic particles of the present invention have a particle diameter distribution of the major axis diameter of 1.5 or less in terms of geometric standard deviation.
It is preferably 0 or less. When the ratio exceeds 1.50, the presence of coarse particles adversely affects the surface smoothness of the coating film, which is not preferable. In consideration of the surface smoothness of the coating film, it is preferably 1.40 or less, more preferably 1.35.
It is as follows. In consideration of industrial productivity, the lower limit of the particle size distribution of the major axis diameter of the obtained acicular nonmagnetic particles containing iron as a main component is 1.01 as a geometric standard deviation.

The needle-shaped nonmagnetic particles containing iron as a main component in the present invention have a resin adsorption strength of 65% or more, preferably 68% or more, more preferably 70% or more.

The high-density acicular hematite particles according to the present invention have a specific surface area S determined by measuring the degree of densification by the BET method.
_{When represented} by the ratio between the _BET value and the specific surface area S _TEM value calculated from the major axis diameter and the minor axis diameter measured from the particles shown in the electron micrograph, have a value of 0.5 to 2.5. I have. In consideration of the surface smoothness of the coating film and the dispersibility in the vehicle, the value of S _BET / S _TEM is preferably from 0.7 to 2.0, more preferably from 0.8 to 1.6.

Incidentally, as the value of S _BET / S _TEM becomes smaller, the densification of the acicular non-magnetic particles containing iron as the main component is achieved, but the particles and the particles adhere to each other by sintering. , The particle size is increased, and the surface smoothness of the coating film tends to be insufficient. When the value of S _BET / S _TEM is increased, it is difficult to say that the density is high enough, many pores are present on the particle surface, and the dispersibility in the vehicle tends to be insufficient.

The non-magnetic underlayer of the magnetic recording medium according to the present invention is obtained by coating a non-magnetic support with a non-magnetic paint containing needle-like non-magnetic particles containing iron as a main component, a binder resin and a solvent. It is obtained by drying after forming a coating film.

Examples of the non-magnetic support include polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamide imide, and the like which are currently widely used for magnetic recording media.
Synthetic resin film such as polyimide, aluminum, metal foils and plates such as stainless steel and various papers can be used, the thickness of which varies depending on the material, but usually preferably 1.0 to 300 μm, more preferably 2.0
２００200 μm. In the case of a magnetic disk, polyethylene terephthalate is usually used as a nonmagnetic support, and its thickness is usually 50 to 300 μm, preferably 6 to 300 μm.
0 to 200 μm. In the case of a magnetic tape, in the case of polyethylene terephthalate, the thickness is usually 3 to 10.
0 μm, preferably 4 to 20 μm, in the case of polyethylene naphthalate, the thickness is usually 3 to 50 μm, preferably 4 to 20 μm, and in the case of polyamide, the thickness is usually 2 to 10 μm, preferably 3 to 7 μm.

In the present invention, the coating thickness of the non-magnetic underlayer after coating and drying the coating composition on the non-magnetic support is in the range of 0.2 to 10.0 μm. If it is less than 0.2 μm, it becomes difficult to improve the surface roughness of the non-magnetic support, and the strength tends to be insufficient. In order to obtain a thin magnetic recording medium, the upper limit is preferably about 10.0 μm, more preferably in the range of 0.5 to 5.0 μm.

As the binder resin, vinyl chloride-vinyl acetate copolymer resin, urethane resin, vinyl chloride-vinyl acetate-maleic acid copolymer resin, urethane elastomer, butadiene Use of acrylonitrile copolymer resin, cellulose derivative such as polyvinyl butyral, nitrocellulose, synthetic rubber resin such as polyester resin and polybutadiene, epoxy resin, polyamide resin, polyisocyanate polymer, electron beam curable acrylic urethane resin, etc. and mixtures thereof. Can be. In addition, each binder resin has -O
_{H, -COOH, -SO 3 M,} -OPO 2 M 2, -NH
A polar group such as ₂ (however, M is H, Na, or K) may be contained. Considering dispersibility of the particles, the polar group -COOH, binder resins that contain -SO ₃ Na are preferred.

The mixing ratio of the powder of the needle-shaped non-magnetic particles mainly composed of iron and the binder resin in the non-magnetic underlayer is such that the needle-shaped non-magnetic particles mainly composed of iron are mixed with 100 parts by weight of the binder resin. Is 5 to 2000 parts by weight, preferably 100 to 100 parts by weight.
0 parts by weight.

A lubricant, an abrasive, an antistatic agent and the like used in the manufacture of a normal magnetic recording medium are added to the nonmagnetic underlayer.
If necessary, it may be added.

The nonmagnetic underlayer according to the present invention containing the acicular nonmagnetic particles containing iron as a main component has a glossiness of the coating film of 170.
To 280%, preferably 180 to 280%, more preferably 185 to 280%, and the coating film surface roughness Ra is 2.0 to 1%.
5.0 nm, preferably 2.0 to 13.0 nm, more preferably 2.0 to 12.0 nm, and a Young's modulus of 125 to 1
50, preferably 127-150, more preferably 13
0 to 150.

The magnetic recording medium is a coating composition comprising, on a non-magnetic underlayer formed on a non-magnetic support, needle-like metal magnetic particles containing iron as a main component, a binder resin and a solvent. Is applied to form a coating film, and then dried to form a magnetic recording layer.

The needle-shaped metal magnetic particles containing iron as a main component in the present invention contain 0.05 to 10% by weight of aluminum in terms of Al.

The location of aluminum may be determined from the central part to the surface if it is contained only in the central part of the needle-shaped magnetic metal particles containing iron as a main component, or if it is contained only in the surface layer part. Either case in which the particles are substantially uniformly contained may be used, or a coating layer may be formed on the surface of the particles, and these various existing positions may be combined. Considering the surface of the magnetic recording layer and the durability of the magnetic recording medium, aluminum is almost uniformly contained from the center to the surface, and the main component is iron whose coating layer is formed on the particle surface. Needle-like metal magnetic particles are preferred.

As is well known, acicular metal magnetic particle powder mainly composed of iron containing aluminum inside
In the production reaction step of the acicular goethite particles described above,
By variously changing the addition time of the aluminum compound, acicular goethite particles containing aluminum are obtained at desired positions inside the particles, and the desired goethite particles or the desired inside of the particles obtained by heating and dehydrating the goethite particles are obtained. At a temperature of 300 to 500 ° C. by heating and reducing acicular hematite particles containing aluminum at the position (1).

The acicular metal magnetic particles containing iron as a main component and having a particle surface coated with aluminum are acicular goethite particles whose particle surface is coated with an aluminum compound such as aluminum oxide or hydroxide. Heating and dehydrating the acicular goethite particles, and heating and reducing the acicular hematite particles having a particle surface coated with an aluminum compound such as an aluminum oxide or hydroxide at a temperature of 300 to 500 ° C. Is obtained by

When the amount of aluminum is 0.0
If the amount is less than 5% by weight, the resin adsorption of the needle-like metal magnetic particles containing iron as a main component in the vehicle is not sufficient,
Dispersion becomes difficult, and a magnetic recording layer or a magnetic recording medium with excellent durability, which is the object of the present invention, cannot be obtained. 10
When the amount exceeds 10% by weight, the effect of improving the durability of the magnetic recording layer and the magnetic recording medium can be recognized, but the effect is saturated and there is no point in having more than necessary. In addition, the magnetic properties of the acicular metal magnetic particles containing iron as a main component are impaired due to an increase in aluminum which is a non-magnetic component.

The needle-like magnetic metal particles containing iron as a main component in the present invention contain 50 to 99% by weight of iron, preferably 6 to 99% by weight.
0 to 95% by weight of the particles.
Co, Ni, P, Si, B, Nd, L other than iron and Al
a, Y, etc. may be contained. Al and Nd, La, Y
When a magnetic recording medium according to the present invention is manufactured using a needle-shaped metal magnetic particle powder containing iron as a main component and a rare earth metal such as a magnetic recording layer having excellent durability, It is preferable because a magnetic recording medium can be easily obtained. In particular, Al and Nd
The most preferred is an acicular metal magnetic particle powder containing iron as a main component.

The acicular metal magnetic particles containing iron as a main component according to the present invention have an average major axis diameter of 0.01 to 0.50 μm.
m, preferably 0.03 to 0.30 μm, and the average minor axis diameter is 0.0007 to 0.17 μm, preferably 0.1 μm.
003 to 0.10 μm and particles having an axial ratio of 3: 1 or more, preferably 5: 1 or more. Considering dispersibility in a vehicle, the upper limit of the axial ratio is 15: 1 or less. , Preferably 10: 1 or less. The shape of the particles may be, for example, a needle shape, a spindle shape, a rice grain shape, or the like.

The magnetic properties of the acicular metal magnetic particles containing iron as a main component have a coercive force of preferably 1200 to 3200 Oe, more preferably 1500 to 2500 Oe, in consideration of characteristics such as high density recording. Saturation magnetization is 100 ~
170 emu / g is preferred, and more preferably 130 to
It is 150 emu / g.

The needle-shaped metal magnetic particles containing iron as a main component in the present invention have a resin adsorption strength of 65% or more, preferably 68% or more, more preferably 70% or more.

As the binder resin in the magnetic recording layer, the binder resin used for forming the nonmagnetic underlayer can be used.

The coating thickness of the magnetic recording layer after applying the coating composition on the nonmagnetic underlayer and drying the coating composition is 0.01 to 5.0.
The range is 0 μm. When the thickness is less than 0.01 μm, it is not preferable because uniform application is difficult and uneven coating is likely to occur. If it exceeds 5.0 μm, it becomes difficult to obtain desired electromagnetic conversion characteristics due to the influence of a demagnetizing field. Preferably it is in the range of 0.05 to 1.0 μm.

The mixing ratio of the acicular metal magnetic particles containing iron as a main component and the binder resin in the magnetic recording layer is such that the amount of the acicular metal magnetic particles containing iron as the main component is 100 parts by weight of the binder resin. Is 200 to 2000 parts by weight, preferably 30
0 to 1500 parts by weight.

The magnetic recording layer may contain commonly used lubricants, abrasives, antistatic agents and the like.

The magnetic recording medium according to the present invention has a coercive force of 9
00-3500 Oe, preferably 1000-3500 Oe
e, more preferably 1500 to 3500 Oe, and a squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) of 0.85 to
0.95, preferably 0.87 to 0.95, the glossiness of the coating film is 180 to 300%, preferably 190 to 300%,
The coating film surface roughness Ra is 12.0 nm or less, preferably 2.
0 to 11.0 nm, more preferably 2.0 to 10.0 n
m, Young's modulus is 130 or more, preferably 132 or more, the linear absorption coefficient of the coating film is 1.10 to 2.00 μm ^−1, preferably 1.20 to 2.00 μm ⁻¹ , and the running durability is 18 Minutes or more, preferably 20 minutes or more, more preferably 22 minutes or more, and the abrasion is B or more, preferably A.

Next, the acicular nonmagnetic particle powder containing iron as a main component according to the present invention, which is a starting material of acicular hematite particles, and the acicular metal containing iron as a main component according to the present invention. A typical basic reaction of acicular goethite particle powder which is also a precursor of magnetic particle powder will be described.

The acicular goethite particles containing aluminum inside the particles are prepared by adding a suspension containing ferrous hydroxide colloid obtained by adding an equivalent or more of an aqueous alkali hydroxide solution to an aqueous ferrous salt solution to a pH of 11 or more. A method of producing needle-like goethite particles by carrying out an oxidation reaction by passing an oxygen-containing gas at a temperature of 80 ° C. or lower, a FeCO obtained by reacting an aqueous ferrous salt solution with an aqueous alkali carbonate solution
A method of producing spindle-shaped goethite particles by oxidizing the suspension containing ₃ as necessary after aging as necessary and then passing an oxygen-containing gas into the aqueous solution of ferrous salt. Needle-like goethite nucleus particles are generated by performing an oxidation reaction by passing an oxygen-containing gas through an aqueous ferrous salt solution containing a ferrous hydroxide colloid obtained by adding an aqueous alkali solution or an aqueous alkali carbonate solution, and then To the aqueous ferrous salt solution containing the acicular goethite core particles, an aqueous alkali hydroxide solution equivalent to or more than Fe ²⁺ in the aqueous ferrous salt solution is added, and then an oxygen-containing gas is passed through to form the acicular aqueous solution. Method for growing goethite core particles and oxygen-containing gas in an aqueous ferrous salt solution containing a ferrous hydroxide colloid obtained by adding an aqueous solution of an alkali hydroxide or an alkali carbonate less than the equivalent of an aqueous ferrous salt solution To generate an acicular goethite nucleus particle by performing an oxidation reaction and then growing the acicular goethite nucleus particle in an acidic to neutral region.

[0078]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical embodiment of the present invention is as follows.
It is as follows.

The average major axis diameter and average minor axis diameter of the particles were determined for about 350 particles shown in a photograph (× 120,000) obtained by magnifying an electron micrograph (× 30000) four times in the vertical and horizontal directions, respectively. The shaft diameter and the short axis diameter were measured respectively, and the average value was shown. The axis ratio is the ratio between the average major axis diameter and the average minor axis diameter.

Geometric standard deviation value (σg) of major axis diameter of particles
Is indicated by a value obtained by the following method. That is, the value obtained by measuring the major axis diameter of the particles shown in the enlarged photograph is calculated from the measured major axis diameter and the actual number of the major axis diameter of the particles, and the horizontal axis is plotted on a lognormal probability paper according to a statistical method. Is plotted as the major axis diameter of the particles, and the ordinate is plotted as a percentage of the cumulative number of particles belonging to each of the predetermined major axis diameter sections (under the integrated screen). The graph shows that the number of particles is 50% and 8%.
The value of the major axis diameter corresponding to each of 4.13% was read, and the geometric standard deviation value (σg) = 84.13 below the integrated screen
% Calculated from the value of the major axis diameter in 50% / the major axis diameter (geometric mean diameter) at 50% below the integrated screen. The smaller the geometric standard deviation value, the better the particle size distribution of the major axis diameter of the particles.

The specific surface area was indicated by a value measured by the BET method.

The degree of densification of the hematite particles was shown by S _BET / S _{TEM as} described above. Where S _BET is
It is the value of the specific surface area measured by the BET method. S
_TEM is a value calculated according to the following formula, assuming that the particles are rectangular parallelepiped, using the average major axis diameter 1 cm and average minor axis diameter wcm of the particles measured from the electron micrograph.

S _TEM (m ² / g) = [(4 lw + 2
w ² ) / (lw ² ρ _p )] × 10 ⁻⁴ (where ρ _p is the true specific gravity of hematite and is 5.2 g /
cm ³ was used. ) S _TEM, since there is absolutely no surface dehydration holes inside the particles and the particle surface is a specific surface area of the smooth particles, S _BET / S _TEM
Is close to 1, it means that hematite particles have few dehydration pores inside and on the surface and have smooth surfaces, in other words, high-density particles.

The amounts of Al, Si, P, B, Ti and Nd present inside and on the surface of the acicular hematite particles were measured by X-ray fluorescence analysis.

The paint viscosity was measured at 25 ° C. using an E-type viscometer EMD-R (manufactured by Tokyo Keiki Co., Ltd.), and the shear rate D was 1.92 sec ^−1.
The values are indicated by

The resin adsorption strength indicates the degree to which the resin is adsorbed on the particles, and the value obtained by the following method is 1
The closer to 00, the more strongly the resin is adsorbed on the hematite particles,
Indicates good.

First, the resin adsorption amount Wa is determined. Particle 20
g and 56 g of a mixed solvent (27.0 g of methyl ethyl ketone, 16.2 g of toluene, 10.8 g of cyclohexanone) obtained by dissolving 2 g of a vinyl chloride-vinyl acetate copolymer resin having a sodium sulfonate group together with 120 g of 3 mmφ steel beads in a 100 ml poly bottle. Add and mix for 60 minutes with a paint shaker.

Next, 50 g of this coating composition was taken out and the
The mixture is placed in a 0 ml settling tube and centrifuged at 10,000 rpm for 15 minutes to separate a solid portion and a solvent portion.
Then, the resin solid content concentration contained in the solvent portion is quantified by a gravimetric method, and the amount of the resin present in the solid portion is obtained by subtracting from the charged resin amount, and this is used as the resin adsorption amount Wa (mg / g) for the particles. And

Next, only the solid portion previously separated was
The whole amount was taken out into a 2 ml tall beaker, and mixed solvent (25.0 g of methyl ethyl ketone, 15.0 ml of toluene)
g, cyclohexanone 10.0 g) and 50 g.
The suspension is placed in a suspended state by ultrasonic dispersion for 5 minutes, and then placed in a 50 ml sedimentation tube and centrifuged at 10,000 rpm for 15 minutes to separate a solid portion and a solvent portion. Then, by measuring the resin solid content concentration in the solvent portion, the amount of resin extracted into the solvent phase among the resin adsorbed on the particle surface is quantified.

Further, the operation from the removal of the total amount of only the solid portion into a 100 ml tall beaker to the determination of the amount of the resin dissolved in the solvent phase was repeated twice, and the total amount of the resin extracted in the solvent phase was totaled three times. We (mg / g) was determined, and the value determined according to the following equation was used as the resin adsorption strength T.
(%).

T (%) = [(Wa−We) / Wa] × 100 The higher the T, the stronger and better the resin adsorption on the powder surface in the vehicle.

The glossiness of the coating surface of the nonmagnetic underlayer and the magnetic recording layer was determined by measuring the 45 ° glossiness of the coating film using “Gloss Meter UGV-5D” (manufactured by Suga Test Instruments Co., Ltd.). Was.

The surface roughness Ra is calculated as follows: “Surfcom-57
The center line average roughness of the coating film was measured using “5A” (manufactured by Tokyo Seimitsu Co., Ltd.).

Regarding the durability of the magnetic recording medium, the following running durability and scratch characteristics were evaluated.

The running durability was measured in “Media Durab”.
ility Tester MDT-3000 ”(St
einberg Associates), a load of 200 gw and a relative speed of 16 between the head and the tape.
Evaluation was made based on the actual operating time at m / s. The longer the actual operating time, the better the running durability.

The scratch characteristics were evaluated by observing the surface of the tape after running with a microscope and visually checking for the presence or absence of scratches.
A rating was given on a scale. A: There is no scratch B: There is some scratch C: There is scratch D: There is severe scratch

The strength of the coating film was determined by measuring the Young's modulus of the coating film using “Autograph” (manufactured by Shimadzu Corporation). Young's Modulus is a commercial videotape "AV T-120
(Manufactured by Victor Company of Japan, Ltd.) ". The higher the relative value, the better.

The magnetic characteristics are described in "Vibration sample magnetometer VSM-
3S-15 "(manufactured by Toei Industry Co., Ltd.) using an external magnetic field of up to 10 KOe.

The degree of light transmission is described in “Self-Recording Photoelectric Spectrophotometer U
V-2100 "(manufactured by Shimadzu Corporation) was used to calculate the light transmittance of the magnetic recording medium, and the resulting value was inserted into the following equation to calculate the linear absorption coefficient. The larger the linear absorption coefficient is, the harder it is to transmit light.

In measuring the light transmittance, the same non-magnetic support as the non-magnetic support used for the magnetic recording medium was used as a blank.

Linear absorption coefficient (μm ⁻¹ ) = ln (1 / t) / FT t: light transmittance at λ = 900 nm (−) FT: coating layer of film used for measurement (thickness of nonmagnetic underlayer) (Sum of thickness of magnetic recording layer and thickness of magnetic recording layer) (μm)

The thicknesses of the non-magnetic support, the non-magnetic underlayer, and the magnetic recording layer constituting the magnetic recording medium were measured as follows.

Digital electronic micrometer K351C
First, the film thickness (A) of the nonmagnetic support is measured using (manufactured by Anritsu Electric Co., Ltd.). Next, the thickness (B) of the nonmagnetic support and the nonmagnetic underlayer formed on the nonmagnetic support
(Sum of the thickness of the nonmagnetic support and the thickness of the nonmagnetic underlayer)
Is measured in the same manner. Further, the thickness (C) of the magnetic recording medium obtained by forming the magnetic recording layer on the nonmagnetic underlayer (the sum of the thickness of the nonmagnetic support, the thickness of the nonmagnetic underlayer, and the thickness of the magnetic recording layer) ) Is measured in the same manner. The thickness of the nonmagnetic underlayer is indicated by BA, and the thickness of the magnetic recording layer is indicated by CB.

<Production of Acicular Goethite Particle Powder> Using an aqueous solution of ferrous sulfate, an aqueous solution of aluminum sulfate, and an aqueous solution of sodium carbonate, 3.89% by weight of aluminum in terms of Al obtained by the above-mentioned method for producing goethite particles. (Average major axis diameter 0.141 μm, average minor axis diameter 0.0181)
μm, axial ratio 7.79, BET specific surface area value 146.8 m ²
/ G and a geometric standard deviation of 1.32) 1380 g were obtained.

This was filtered with a press filter, washed with pure water until the electric conductivity became 30 μs or less, then dried and pulverized to obtain acicular goethite containing aluminum uniformly inside the particles. Particles were obtained. Here, when the resin adsorption strength was measured, it was 63.8%. This was used as a nonmagnetic particle powder of a nonmagnetic underlayer A described later.

<Production of low-density acicular hematite particle powder>
1200 g of the acicular goethite particle powder was suspended in water to form a slurry, and the solid content concentration was adjusted to 8 g / l. Heat 150 liters of this slurry to a temperature of 60 ° C., add 0.1N NaOH aqueous solution and adjust the pH
The value was adjusted to 9.0.

Next, 30.0 g of No. 3 water glass as a sintering inhibitor was gradually added to the alkaline slurry, and after the addition was completed, aging was performed for 60 minutes. Next, a 0.1 N acetic acid solution was added to the slurry to adjust the pH value of the slurry to 6.0. Thereafter, filtration, washing, drying and pulverization were carried out by a conventional method to obtain acicular goethite particle powder in which a silicon oxide was coated on the particle surface. SiO ₂
The amount was 0.70 wt%.

One of the obtained acicular goethite particle powders
000 g was put into a stainless steel rotary furnace, and heat-treated at 330 ° C. for 60 minutes in the air while being driven to rotate to dehydrate, thereby obtaining low-density acicular hematite particles.

Next, 100 g of the obtained low-density acicular hematite particles were peptized in 1 liter of pure water using a homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.), and then filtered and purified using Nutsche. Washing was performed using water until the electric conductivity became 30 μs or less. Thereafter, drying and pulverization were performed to obtain low-density hematite particles.

The low density acicular hematite particles containing aluminum obtained had an average major axis diameter of 0.108 μm,
Average short axis diameter 0.0161 μm, axial ratio 6.70, BET specific surface area value (S _BET ) 186.5 m ² / g, density S
_BET / S _TEM : 3.63, Al content: 4.27% by weight
And the geometric standard deviation value was 1.35. The resin adsorption strength was 68.8%. This hematite was used as a non-magnetic particle powder of a non-magnetic underlayer B described later.

<Production of high-density acicular hematite particle powder>
850 g of the above low-density acicular hematite particle powder is charged into a ceramic rotary furnace, and is driven to rotate in air.
Heat treatment was performed at 0 ° C. for 30 minutes to seal dewatered holes.

Next, 100 g of the obtained high-density acicular hematite particles were peptized in 1 liter of pure water using a homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.), and then filtered and purified using Nutsche. Washing with water was carried out using water until the electric conductivity ° C became 30 µs or less. Thereafter, drying and pulverization were performed to obtain high-density acicular hematite particles.

The high-density acicular hematite particles have an average major axis diameter of 0.107 μm, an average minor axis diameter of 0.0162 μm, an axial ratio of 6.60, and a BET specific surface area (S _BET ) of 58.0.
m ² / g, the degree of _{densification} S _BET / S _TEM was 1.14, and the geometric standard deviation value was 1.36. The Al content is 4.
It was 30% by weight. The resin adsorption strength is 71.6%
Met. This hematite was used as a nonmagnetic particle powder of a nonmagnetic underlayer C described later.

<Production of Nonmagnetic Underlayer> Using the acicular goethite particle powder, low-density acicular hematite particle powder and high-density acicular hematite particle powder obtained above, 12 g of each particle powder and a binder resin solution ( A mixture (30% by weight of vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group and 70% by weight of cyclohexanone) and cyclohexanone are mixed to obtain a mixture (solid content: 72%), and this mixture is further kneaded with a plastmill for 30 minutes. Thus, three kinds of kneaded materials were obtained.

Each of the three types of kneaded materials was placed in a 140 ml glass bottle, and 95 g of 1.5 mmφ glass beads, a binder resin solution (30% by weight of a polyurethane resin having a sodium sulfonate group, and a solvent (methyl ethyl ketone: toluene =
1: 1) 70% by weight), cyclohexanone, methyl ethyl ketone and toluene, and mixed and dispersed for 6 hours with a paint shaker to obtain three kinds of coating compositions.

The composition of the paint containing each of the obtained acicular goethite particle powder, low-density acicular hematite particle powder and high-density acicular hematite particle powder was as follows.

Acicular goethite particle powder, low-density acicular hematite particle powder, or high-density acicular hematite particle powder 100 parts by weight Vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group 10 parts by weight Sodium sulfonate group Polyurethane resin having 10 parts by weight Cyclohexanone 44.6 parts by weight Methyl ethyl ketone 111.4 parts by weight Toluene 66.9 parts by weight

Each of the three paints obtained was applied to a thickness of 12 μm.
m was applied on a polyethylene terephthalate film having a thickness of 55 μm using an applicator, and then dried to form three types of nonmagnetic underlayers. The thickness of each of the nonmagnetic underlayers was 3.5 μm.

The nonmagnetic underlayer A obtained when the acicular goethite particle powder was used as the nonmagnetic particle powder had a gloss of 185%, a surface roughness Ra of 11.8 nm, and a Young's modulus (relative Value) was 131.

The non-magnetic underlayer B obtained by using low-density acicular hematite particle powder as the non-magnetic particle powder has a gloss of 189%, a surface roughness Ra of 11.0 nm, and a Young's modulus (relative Value) was 132.

The nonmagnetic underlayer C obtained by using high-density acicular hematite particle powder as the nonmagnetic particle powder has a gloss of 215%, a surface roughness Ra of 7.6 nm, and a Young's modulus (relative Value) was 135.

<Production of Magnetic Recording Layer> 0.74% by weight in terms of Al in the center of the grains and 0.39% in terms of Al in the surface layer.
Acicular metal magnetic particles containing iron as a main component and containing aluminum by weight (average major axis diameter 0.113 μm, average minor axis diameter 0.0185 μm, axial ratio 6.11, coercive force 18)
80 Oe, saturation magnetization value 128 emu / g, geometric standard deviation 1.36, resin adsorption strength 75.1%) 12 g, abrasive (trade name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) 1.2
g, carbon black (trade name: # 3250B, manufactured by Mitsubishi Kasei Corporation) 0.36 g, binder resin solution (30% by weight of vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group and 70% by weight of cyclohexanone) And cyclohexanone to obtain a mixture (solid content: 78%). This mixture was further kneaded with a plastmill for 30 minutes to obtain a kneaded product.

The kneaded material was placed in a 140 ml glass bottle for 1.5 times.
glass beads 95 g, binder resin solution (polyurethane resin having sodium sulfonate group 30% by weight,
A solvent (methyl ethyl ketone: toluene = 1: 1) 70% by weight), cyclohexanone, methyl ethyl ketone and toluene were added, and the mixture was mixed and dispersed with a paint shaker for 6 hours to obtain a magnetic paint. Thereafter, a lubricant and a curing agent were added, and the mixture was further mixed and dispersed with a paint shaker for 15 minutes.

The composition of the obtained magnetic paint was as follows. Metal magnetic particle powder mainly composed of iron 100 parts by weight Vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group 10 parts by weight Polyurethane resin having sodium sulfonate group 10 parts by weight Abrasive (AKP-30) 10 parts by weight Parts Carbon black (# 3250B) 3.0 parts by weight Lubricant (myristic acid: butyl stearate = 1: 2) 3.0 parts by weight Curing agent (polyisocyanate) 5.0 parts by weight Cyclohexanone 65.8 parts by weight methyl ethyl ketone 164 0.5 parts by weight Toluene 98.7 parts by weight

The magnetic paint was applied to the non-magnetic underlayers A, B and C
After applying to a thickness of 15 μm on each of the above using an applicator, orienting and drying in a magnetic field, and then performing a calendering process, a curing reaction at 60 ° C. for 24 hours to obtain a 0.5 inch width The magnetic tape was obtained by slitting. The thickness of each of the magnetic recording layers was 1.1 μm.

The magnetic tape obtained by forming the magnetic recording layer on the non-magnetic underlayer A had an Hc of 1950 Oe, a squareness ratio (Br / Bm) of 0.87, a glossiness of 195%, and a surface roughness of 195%. Degree Ra is 10.8 nm, Young's modulus (relative value) is 13
5, the linear absorption coefficient is 1.21, the running durability is 21.6 minutes,
The scratch characteristics were B.

The magnetic tape obtained by forming the magnetic recording layer on the non-magnetic underlayer B had an Hc of 1961 Oe, a squareness ratio (Br / Bm) of 0.87, a glossiness of 199%, and a surface roughness of 199%. Degree Ra is 10.0 nm, Young's modulus (relative value) is 13
4, the linear absorption coefficient is 1.25, the running durability is 23.6 minutes,
The scratch characteristics were A.

A magnetic tape obtained by forming a magnetic recording layer on the non-magnetic underlayer C has a Hc of 1973 Oe, a squareness ratio (Br / Bm) of 0.88, a glossiness of 221% and a surface roughness of 221%. Degree Ra is 7.8 nm, Young's modulus (relative value) is 135,
The linear absorption coefficient was 1.26, the running durability was 29.6 minutes, and the scratch characteristics were A.

[0129]

The most important point in the present invention is that non-magnetic particle powder containing 0.05 to 50% by weight of aluminum in terms of Al in the inside of the particle, and, if necessary, a hydroxide of aluminum and a powder of aluminum. Oxide, a hydroxide of silicon and a needle-shaped non-magnetic particle powder mainly composed of iron whose particle surface is coated with at least one of silicon oxide and non-magnetic particles for the non-magnetic underlayer, A
When the needle-like metal magnetic particle powder containing iron as a main component and containing 0.05 to 10% by weight of aluminum in terms of 1 is used as the magnetic particle powder for the magnetic recording layer, the surface of the non-magnetic underlayer is Smoothness and strength of the substrate can be improved,
When a magnetic recording layer is provided on the non-magnetic underlayer, to obtain a magnetic recording medium having a low light transmittance of the magnetic recording layer, a smooth surface, a high strength, and excellent durability. The fact is that you can.

Regarding the reason why the surface smoothness of the non-magnetic underlayer and the strength of the base were able to be further improved, the present inventor explained that the binder resin in the vehicle of the non-magnetic particles was It is thought that the adhesion of the non-magnetic particles and the non-magnetic underlayer in the non-magnetic underlayer to the non-magnetic support was increased as a result.

Although the reason why the durability of the magnetic recording medium has been improved is not yet clear, as shown in the following examples,
The present inventor has used acicular goethite particles or acicular hematite particles in which aluminum is uniformly contained inside the particles as non-magnetic particles, and an acicular metal mainly containing iron in which aluminum exists. Due to the synergistic effect with the use of the magnetic particle powder as the magnetic particles, the resin adsorption strength between the non-magnetic particles and the magnetic particles and the binder resin in the vehicle increases, and as a result, the non-magnetic underlayer Synergistic effects such as increased adhesion of the non-magnetic particles and the non-magnetic underlayer itself to the non-magnetic support, and increased adhesion of the magnetic particles and the magnetic recording layer itself to the non-magnetic under layer in the magnetic recording layer I think it is due to.

[0132]

Next, examples and comparative examples will be described.

<Types of Acicular Goethite Particle Powder> Non-magnetic Particles A1 and A8
Two types of acicular goethite particle powders containing aluminum uniformly inside particles having different amounts of aluminum contained, degree of densification, presence / absence of surface coating, resin adsorption strength, etc. were prepared.

Tables 1 and 2 show the properties of the acicular goethite particle powders A1 and A8.

<Types of Acicular Hematite Particle Powder> Basic production reaction, kind, and content of acicular goethite particle powder in which nonmagnetic particles A2 to A7 and A9 to A11 uniformly contain aluminum inside the starting material particles. Needle-like hematite particles containing aluminum uniformly inside particles with various differences in the amount of aluminum, type and amount of sintering inhibitor, degree of densification, presence / absence, amount, type and resin adsorption strength of the surface coating Powder was prepared.

Acicular hematite particles A2 to A7, A9 to A
Table 1 and Table 2 show various characteristics of No. 11.

[0137]

[Table 1]

[0138]

[Table 2]

The surface coating treatment of the acicular non-magnetic particles was carried out by the following method except that the type of the non-magnetic particles and the type and amount of the coating were variously changed.

5 l of a slurry containing non-magnetic particles A4 having a concentration of 98 g / l was heated to 60 ° C., and 199.6 ml of a 1.0 N NaAlO ₂ solution was added to the slurry (19.6 ml of Al in terms of Al with respect to acicular goethite particles). .1% by weight), and after holding for 30 minutes, the pH was adjusted using acetic acid.
The value was adjusted to 7.5. Next, in the same manner as in the embodiment of the present invention, filtration, washing with water, drying, and pulverization were performed to obtain acicular goethite particle powder having a particle surface covered with a coating.

<Production of Non-Magnetic Underlayer> Examples 1 to 7 and Comparative Examples 1 to 4 Non-magnetic particles were prepared in the same manner as in the embodiment of the present invention by using acicular non-magnetic particles of non-magnetic particles A1 to A11. A magnetic underlayer was obtained.

Table 3 shows the main manufacturing conditions and various characteristics at this time.

[0143]

[Table 3]

<Manufacture of Magnetic Recording Medium> Examples 8 to 24 and Comparative Examples 5 to 13 First, four types of metal magnetic particle powders containing iron as a main component shown in Table 4 were prepared.

[0145]

[Table 4]

Except that the type of the nonmagnetic underlayer and the type of the acicular metal magnetic particles containing iron as the main component were variously changed, the metal containing iron as the main component was used in the same manner as in the embodiment of the present invention. A magnetic recording medium using magnetic powder was manufactured.

The main manufacturing conditions and various characteristics at this time are shown in Tables 5 and 6.

[0148]

[Table 5]

[0149]

[Table 6]

[0150]

The magnetic recording medium according to the present invention has a strength as a substrate, because it is a non-magnetic powder containing aluminum almost uniformly inside the particles, as described in the above embodiment. A magnetic recording medium having a low light transmittance, a smooth surface, and a high strength when a magnetic recording medium is formed using the nonmagnetic underlayer. In addition, the magnetic recording medium uses needle-like non-magnetic particle powder containing aluminum uniformly inside the particles as the non-magnetic particle powder for the non-magnetic underlayer. Since it is excellent in durability due to the use of needle-like metal magnetic particle powder containing iron as a main component in which aluminum exists as a powder, it is preferable as a magnetic recording medium for high density recording. .

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Hiroko Morii 4-1-2, Funariminami, Naka-ku, Hiroshima-shi, Hiroshima Toda Kogyo Co., Ltd.

Claims (2)

[Claims] 1. A nonmagnetic underlayer containing a nonmagnetic support, a nonmagnetic particle powder formed on the nonmagnetic support, and a binder resin, and a magnetic particle powder formed on the nonmagnetic underlayer bonded to the nonmagnetic underlayer. A non-magnetic particle powder in an amount of 0.05 to 5 in terms of Al.
A needle-shaped nonmagnetic particle powder containing iron as a main component containing 0% by weight of aluminum inside the particle, wherein the magnetic particle powder contains 0.05 to 10% by weight of aluminum in terms of Al. A magnetic recording medium characterized by acicular metal magnetic particles containing iron as a main component. 2. A non-magnetic base layer containing a non-magnetic support, non-magnetic particle powder formed on the non-magnetic support, and a binder resin, and a magnetic particle powder formed on the non-magnetic base layer are bonded. A non-magnetic particle powder in an amount of 0.05 to 5 in terms of Al.
Iron containing 0% by weight of aluminum in the interior of the particle and having at least one of aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide on the surface of the particle. A needle-shaped non-magnetic particle powder as a component, wherein the magnetic particle powder is 0.05% in terms of Al.
A magnetic recording medium, which is a needle-shaped metal magnetic particle powder containing iron as a main component and containing 10 to 10% by weight of aluminum.